System of control.



R. E. HELLMUND.

SYSTEM OF CONTROL. APPLICATION FILED SEPT, 13, ms.

Patented Nov. 26, 1918.

2 SHEETSSHEEY I.

WITNESSES:

- ATTORNEY RJE. HELLMU ND.

( SYSTEM OF CQ'NTROL.

APPLICATION FILED SEPT. 13. Hill).

1,285,698. Patented Nov. 26, 1918.

. 2 SHEETS$HEET Z.

WITNESSEIS: INVENT W fluao/f law/mu (mwe/ ATTORNEY UNITED srra'r zs PLJTENT OFFICE.

RUDOLF E. HELLMUND, 0F SWISSVALE, PENNSYLVANIA, ASSIGNOR TO WESTINGHOUSE ELECTRIC AND MANUFACTURING- COMPANY, A CORPORATION OF PENNSYLVANIA.

SYSTEM OF CONTROL.

Specification of Letters Patent.

Patented Nov. 26, 1918.

To all whom it may concern:

Be it known that I, Rononr E. HELLMUND, a subject of the Emperor of Germany, and a resident of Swissvale, in the county of Allegheny and State of Pennsylvania, have invented a new and useful Improvement in Systems of Control, of which the following is a specification.

My invention relates to systems of control for induction motors which may be employed from time to time as recuperative generators, as, for example, in electric railway or hoisting systems, and it has for its object to provide a system of the character designated wherein the adjustment of the motors, throughout the accelerating and decelerating speed ranges, may be effected in a smooth and simple manner, with a mini mum energy loss.

Other objects of my invention will hereinafter more fully appear.

Referring to the accompanying drawings, Figure 1 is a diagrammatic view of two dynamo-electric machines of the induction type, together with a frequency-changer and other auxiliary apparatus, arranged to be operated in accordance with my invention; Fig. 2 is a sequence chart illustrating a preferred order of switch operation in the system of Fig. 1; Fig. 3 is a diagrammatic view of a control system arranged to operate the switches of the system of Fig. 1 in the order indicated in Fig. 2; Fig. 1 is a detail view of an electromagnetic switch of ordinary type suitable for employment in the system of Fig. 1; and Figs. 5 to 8, inclusive, are simplified diagrammatic views of the system of Fig. 1 illustrating the development of the connections therein. when the switches thereof are operated inthe order set forth in the chart of Fig. 2.

In my copending application, Serial No. 69,189, filed December 29, 1915, I disclose and claim a system wherein a frequency changer and an adjustable transformer are associated with an induction motor for the speed regulation thereof. At the outset, said frequency-changer and transformer are connected between the source and the rotor winding of said motor, operating as a primary member, the stator winding of said motor being closed upon itself for operation as a secondary member. The stator winding is then connected to the source for operation as a primary member, and said frequency-changer and adjustable transformer are maintained in circuit between the rotor winding, now acting as a secondary member, and the source for speed adjustment up to, through and above synchronism. By this means, I am enabled to employ a frequency-changer having substantially onehalf the capacity of the motor for the speed control of the motor from zero to 150% of synchronism.

In the present system, I employ the same basic idea for the control of two induction motors mounted, for example, on a railway vehicle, providing, in addition, means for non-concurrently interchanging the function of the two windings in each motor and, furthermore, providing not only for speed control during motor operation but for recuperative current control during recuperative operation.

In the drawing, I show two induction motors at 18 and 19, respectively, in Fig. l. The motor 18 is provided with a three-phase, Y-con'nected stator winding 20 and with a rotor 21 hearing a three-phase Y-connected winding 22, the terminals of which are connected to suitable slip rings 23. In like manner, the motor 19 is provided with a stator winding 24 and with a rotor 25 hearing a winding .26 connected to suitable slip rings 27 Energy for the operation of the motors 18 and 19 is derived from a suitable singlephase trolley 28 through an auto-transformer 29, as is usual in single-phase railway systems. The motors 18 and 19 being of the polyphase type for facilitating starting and control, the single-phase energy of the trolley 23 is converted into polyphase form by a phase-converter 30 of any suitable type and supplied to polyphase buses 31.

A frequency-changer 32, of well known type, is provided and comprises an armature 33 provided with both commutator and slip rings and with a stator winding 341 arranged to be closed through an adjustable resistor 35. The slip rings of the frequency changer 32 may be connected to the buses 31 through an adjustable transformer 50 and suitable switches 7, 8 and 9. The brushes of the commutator of the machine 32 are in connection with suitable brushes bearing re spectively on the slip rings 23 and 27. The direction of phase rotation between the frequency changer 33 andthe motor 18 may be reversed by a suitable switch 36 and, in like manner, the direction of phase rotation between the frequency changer 32 and the motor 19 may be reversed by a suitable switch 37. p

The rotor windings 22 and 26 may be closed through resistors 38 and 39 by the manipulation of suitable switches 16 and 17 or said windings may be closed directly upon themselves by the operation of suitable switches 14 and 15.

The primary winding 20 of the motor 18 may be connectedto the buses '31by suitable switches 1,2 and 3 or said winding may be closed u onitself by suitable switches 10 and 11. 11 like manner. the stator winding 24 of the motor 19 maybe connected directly to the buses 31 throu h suitable switches 4:, 5 and 6 or said win" ing may be closed upon itself through switches 12 and 13.

The different switches 1 to 17, inclusive, may be of any desired type, either manually or automatically controlled and, if of the automatic'type, they may be either electroniagnetically or pneumatically operated. A preferred type is shown in Fig. 4. In Fig. 3, I have indicated operating coils 1 to 17*, inclusive, for said switches, said operating coils being energized through suitable contact studs 4t04.-0 from a control battery 41 by the operation of a master controller bearing suitable accelerating segments 42-42 and recuperative segments 43 "Having thus described the arrangement of a system embodying my invention, the operation is as follows: The controller of Fig. 3 is'fir'st moved to the position A, closing the switches 7, 8 and 9 and connecting the transformer to the buses 31 which are assumed to have been energized by suitable polyphase current from the transformers 29 and the phase converter 30. The transformer 50 and the resistor-'35 are so adjusted that the output of the machine 32, at its connnutator end, is of low frequency and low voltage. The switches 36 and 37 are so manipulated that the direction of phase rotation of the polyphase currents supplied from the machine 32 to the rotor windings 22 and 26 is opposite to the direction in which it is desired to have the motors 18 and 19 operate; that is to say, if the vehicle is to move in such a direction' that the motors 18 and 19are to rotate clockwise, the direction of phase rotation in the windings 22 and 26 should be counter-clockwise.

The controller of Fig. 3 is next moved to position B, operating the switches 10, 11. 12 and 13 and closing the stator windings 2024npon themselves. The motors 18 and 19 now rotate very slowly in a clockwise direction, the rotorwindings 22 and 26 an arrow 46 indicates thereof operating as primary windings and the stator windings 20 and 24 operating as secondary windings. The primary windings may be assumed to produce a substantially fixed field in space and the counterclockwise rotating fields of the rotor Windings 22 and 26 react thereagainst, causing the appropriate clockwise rotation of the rotors 21 and The speed of the frequency changer is now raised by the adjustment of the resistor '35, thus increasing the frequency of the alternating currents supplied to the motors 18 and 19 and, concurrently therewith, the transformer 50 is adjusted to raise the voltage-applied to said motors. This process is continued until the motors 18 and 19 have attained substantially 50% of synchronous speed, as determined by the frequency of the main supply, said speed regulation having been effected with comparatively little energy loss. The general type of operation duri ig this phase of the accelerating process is indicated in Fig. 5, a composite arrow 45 indicating the direction of energ flow through the frequency changer 32 to the motors 18 and 19.

Having attained substantially 50% of synchronous speed, the capacity of the machine 32 for supplying energy to the motors 18 and 19is reached, and, accordingly, transition is now made to a cascade connection. The controller of Fig. 3 is first moved to the position C to open the switches 12 and 13, thus deenergizing the motor 19, and the switch 37 is then reversed to interchange two phases of the rotor winding 26. The movement of the controller to the position D- now closes the switches 4-, 5 and 6, connecting the stator winding 24 of the motor 19 directly to the buses 31. for primary operation. The connections completed by the switches 1, 5 and 6 ing field in the stator winding 24- moves in a clockwise direction, dragging with it the rotor winding 26 and producing a clockwise rotation in said stator winding. Pol phase energy from said clockwise rotating winding 26 is supplied to the rotor winding 22 for primary operation thereof, and the direction of phase rotation is reversed at the switch 3 7 so that the rotating field within the winding 22 is still counterclockwise, reacting with the short circuited sta tor winding 20 to continue operation of the motor 18 in the same direction as heretofore. The machine 32 may now be entirely disconnected, if desired, and the motors l8 and 19 operated in concatenation or cascade at substantially 50% of synchronous speed, all as indicated in Fig. 6, wherein the flow of energy throughthe motor 19 to the motor 18.

To stillfurther accelerate the'motors 18 and 19, use is madeof the frequency changer are such that the i'otat- 32 to return energy to the buses 31, rather than to derive energy therefrom. T0 at tain this result, the controller is first moved to the position E to open the switches 10 and 11, thus opening the stator winding 20 of the motor 18, and the switch 36 is then reversed to interchange two phases of the rotor winding 22. The movement of the controller to the position F now closes the switches 1, 2 and 3, connecting the stator Winding 20 of the motor 18 to the buses 81 for primary operation. Both motors 18 and 19 now operate in the usual manner, with their stator windings connected to the source for primary operation and with their rotor windings returning energy to the source through the frequency changer 32, rather than dissipating said energy in rheostatic losses. The speed of the machine 32 is now reduced, by manipulation of the resistor 35, and the voltage thereof is reduced by adjusting the transformer 50, thus reducing the amount of energy returned to the source and increasing the amount available for the motors 18 and 19, bringing the motors up to substantially synchronous speed. The general arrangement of 'COIHXEQUODS during this phase of the accelerating proc ess is indicated in Fig. 7, the general flow of energy through the motors back to the source through the machine 32 being indicated by a composite arrow 17 Having attained substantially synchronous speed, the movement of the controller ofFig. 3 to the position G first closes the switches 16 and 17, closing the rotor circuits 22 and 26 through the resistors 38 and 39, then opening the switches 7 8 and 9, deenergizing the machine 32, and finally operating the switches 14: and 16, closing the resistor windings 22 and 26 upon themselves for ordinary slip operation of the induction motors. The action is now indicated in Fig. 8, the flow of energy to the two motors 18 and 19 being indicated by suitable arrows 18 and 49.

If it now be desired to operate the motors 18 and 19 at over-synchronous speeds, they may be carried through synchronism in any Well known manner and the switches 36 and 37 again reversed, thus reversing the direction of phase rotation in the windings 22 and 26. The frequency and voltage of the machine 32 is then slowly increased, as during the initial stages of operation, and the reaction of the counter-clockwise rotating field of the rotor windings against the synchronously rotating clockwise rotation of the stator fields produces the desired oversynchronous operation.

It will be observed that, during the entire above described accelerating operation, means have been provided for a smooth and gradual increase in the speed and, at no time, has it been necessary to dissipate more 18 and 19 and than a negligible amount of energy in rheostatic losses. Particular attention is directed to the fact that the various transitions are provided for only one motor at a time, thus still further enhancing the smoothness of the accelerating process.

If it be desired to recuperate energy as, for example, when descending grades or when stopping the vehicle, the above sequence of operations may be reversed. It is unnecessary to go into the recuperative connections in great detail, the order and manner of adjustment, in each case, being the converse of that just disclosed and the flow of energy in the different connections being the reverse of that indicated by the arrows 15 to 19, inclusive, in Figs. 5 to 8. If recuperation is desired at over-synchronous speed, as, for example, between synchronism and 150% synchronism, the frequency changer may be so arranged by the manipulation of the switches 36 and 37 that its frequency and voltage shall be subtracted from the frequency and voltage of the motors 18 and 19, respectively, leaving a residual voltage of such magnitude as to produce the desired braking current. At under-synchronous speeds, the frequency changer 32 is first reintroduced at low frequency and low voltage, serving to boost the output voltage of the motors 18 and 19 the small amount that is necessary for recuperation when operating slightly below synchronous speed, the switches 14 to 17 inclusive, being open. As the speed of the vehicle decreases, the voltage and frequency boost of the machine 32 is still further increased until the motors 18 and 19 are operating at substantially 50% of synchronous speed when, by the establishment of the cascade connections of Fig. 6, the two motors may generate in cascade, the output of the motor 18 being at substantially one-half the voltage and one-half the frequency of the buses 31 and being boosted, both in frequency and in voltage, by passage through the motor 19 for superposition upon the buses.

For still lower speeds, the connections of Fig. 5 are reestablished, the entire output of the motors 18 and 19 returning to the buses 31 through the machine 32 and the transformer 50, being suitably converted thereby, both in frequency and voltage, for producmg the desired recuperative current.

I have indicated the use of a frequency changer of usual. type, but, obviously, I may employ, in lieu thereof, any desired type of equivalent apparatus whereby the relatively high frequency of the source may be adapted for application to a low-frequency rotor or vice versa and, in the subjoined claims, I employ the term frequencychanger in its broadest sense to imply any form of apparatus capable of performing the desired function.

While I have shown my invention in its preferred forms, it will be obvious to those skilled in the art that it is susceptible of various minor changes and modifications without departing from the spirit thereof and I desire, therefore, that only such limitations shall be placed thereupon as are imposed by the prior art or as are set forth in the appended claims.

I claim as my invention:

1. The combination with a source of al ternating current, of a plurality of induction motors, a frequency changer, means whereby said frequency-changer may supply energy to one member of each of said motors as a primary member in starting, the other member of each motor operating as a secondary member, means whereby said motors may be operated in cascade at higher speeds, and means whereby each of said motors may derive energy directly from the source to return a portion of said energy thereto through said frequency-changer at still higher speeds.

2. The combination nvith a source of alternating current, of a plurality of induction motors, a frequency changer, means whereby said frequency-changer may sup ply energy to one member of each of said motors as a primary member in starting, the other member of each motor operating as a secondary member, means whereby said motors may be operated in cascade at higher speeds, and means whereby each of said motors may derive energy directly from the source to return a portion of said energy thereto through said frequency changer at still higher speeds, the functions of the two members of each motor being interchanged with reference to their initial conditions.

3. The combination with a source of alternating current, of a plurality of induction motors, a frequency-changer, means whereby said frequency-changer may supply energy to one member of each of said motors as a primary member in starting, the other member of each motor operating as a secondary member, means whereby said motors may be operated in cascade at higher speeds, means whereby each of said motors may derive energy directly from the source to return a portion of said energy thereto through said frequency-changer at still higher speeds, and means whereby all of said motors may be connected directly to said source for independent operation at maximum speed.

f. The combination with a source of alternating current, of a plurality of induc tion motors, a frequency changer, and means whereby said frequency-changer may supply energy to one member of each of said motors as a primary member in starting, the other member of each motor operating as secondary, whereby said motors may be operated in cascade at higher speeds, and each of said motors may derive energy directly from the source to return a portion of said energy thereto through saidfrequency changer at still higher speeds, the functions of the two members of each motor being interchanged with reference to their initial conditions.

5. The method of operating a frequency changer in conjunction with a source of alternating current and two induction motors which comprises initially connecting said frequency changer to supply energy from said source to the primary windings of said motors, while short-circuiting the secondary windings thereof, then operating said motors in cascade from said source and finally operating both of said motors from said source, returning a portion of the energy supplied to said motor to said source through said frequency changer.

6. The method of operating a frequencychanger in conjunction with a source of alternating current and two induction motors which comprises initially connecting said frequency changer to supply energy from said source to the primary windings of said motors while short-circuiting the secondary windings thereof, then operating said motors in cascade from said source, then operating both of said motors from said source, returning a portion of the energy thereof to said source through said frequency changer and finally operating both of said motors directly from said source, with short-circuited secondary windings.

7. The method of operating a frequencychanger in conjunction .with a source of alternating current and two induction motors which comprises initially connecting said frequency-changer to supply energy from said source to the prinrary windings of said motors while shoit-circuiting the secondary windings thereof. interchanging the functions of the two windings of one of said motors, operating said two motors in cascade, with said motor connected to the source and then operating said two motors directly from said source .while returning energy from the secondary windings thereof to said source through said frequency changer.

8. The method of operating a frequency changer in conjunction with a source of a1- ternating current and two induction motors which comprises initially connecting said frequency changer to supply energy from said source to the primary windings of said motors while short-cireuiting the secondary windings thereof, interchanging the functions of the two windings of one of said motors, operating said two motors in cascade, .with said motor connected to the source, interchanging the functions of the two windings of theother motor and-then operating said two motors directly from said source while returning energy from the secondary windings thereof to said source through said frequency changer.

9. The method of operating a frequency changer in conjunction with a source of alternating current and two induction motors which comprises initially connecting said frequency changer to supply energy from said source to the primary windings of said motors while short-circuiting the secondary windings thereof, interchanging the functions of the two windings of one of said motors, operating said two motors in cascade, with said motor connected to the source, operating said two motors directly from said source while returning energy from the secondary wlnding thereof to said source through said frequency-changer and finally operating both of said motors directly from said source with short-circuited secondary members.

10. The method of operating a frequency changer in conjunction with a source of alternating current and two induction motors which comprises initially connecting said frequency changer to supply energy from said source to the primary windings of said motors while short-circuiting the secondary windings thereof, interchanging the functions of the two windings of one of said motors, operating said two motors in cascade, with said motor connected to the source, interchanging the functions of the two windings of the other motor, operating said two motors directly from said source while returning energy from the secondary windings thereof to said source through said frequency changer and finally operating both of said motors directly from said source, with short circuited secondary members.

11. The method of recuperating energy in a system embodying two induction motors, variable speed driving means therefor, a frequency changer, and a source of alternating current which comprises connecting each of said motors directly to said source, as an induction generator, at high speed, maintaining said connection while supplying energy to the secondary members of said motors Copies of this patent may be obtained for five cents each, by addressing the from said source through said frequency changer to maintain the recuperative voltage at the supply value at lower speeds, and thereafter connecting said motors in cascade at still lower speeds.

12. The method of recuperating energy in a system embodying two induction motors, variable-speed driving means therefor, a frequency changer, and a source of alternating current which comprises connecting each of said motors directly to said source as an induction generator, at high speed, maintaining said connection while supplying energy to the secondary members of said motors from said source through said frequency changer to maintain the recuperative voltage at the supply value at lower speeds, thereafter connecting said motors in cascade at still lower speeds, and finally connecting both of said motors to supply energy to said source through said frequency changer.

13. The method of recuperating energy in a system embodying two induction motors, variable speed driving means therefor, a frequency changer, and a source of a1ternating current which comprises connecting each of said motors directly to said source as an induction generator at a certain speed, supplying energy to the secondary members thereof from said source through said frequency changer to raise the output voltage thereof, and thereafter interchanging the functions of the two windings of one of said motors and then connecting said motors in cascade to said source at lower speeds.

1 1. The combination with a source of alternating current, of two induction motors, a frequency changer, and means for employing said frequency changer to supply energy to the primary windings of both motors from said source at times, and for employing said frequency changer to supply energy to the secondary windings of each machine at other times, the means for effecting changeover in one machine being independently operable from the means for efiecting changeover in the other machine.

In testimony whereof, I have hereunto subscribed my name this 25th day of August, 1916.

RUDOLF E. HELLMUND.

Commissioner or Iatents,

Washington, D. 0. 

